Supporting structure for electric discharge lamps



D 1949 I E. c. 'MARTT 2,491,868

SUPPORTING STRUCTURE FOR ELECTRIC DISCHARGE LAPS 7 Filed July 29, 1948 Fig 5.

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fiatented Dec. 20, 1949 2.491.888 surron'rmo STRUCTURE FOR ELECTRIC DISCHARGE LAMPS I Ernest C. Mutt. Cleveland,

kEleetrie Company,

General New Yor Ohio, assignor to a corporation oi Application J uly 29, 1948, Serial No. 41,379 2 Claims. (01. 176-122) My invention relates to high pressure mercury vapor discharge lamps of the type having an arc tube mounted in an outer envelope and its prin cipal object is to provide a simple, strong, rugged support for the tube in the envelope.

Other objects and advantages of the invention will appear from the following description of species thereof taken in conjunction with the accompanying drawing in which Fig. 1 is a perspec tive view of a lamp embodying my invention with part of the outer envelope broken away to show the inner arc tube and its support; Fig. 2 is a bottom plan view of an element of the arc tube support; and Fig. 3 is an elevational view on a smaller scale of an outer envelope of a difierent shape and in which the arc tube and its supportshown in Figs. 1 and 2 may be mounted.

Referring to Figs. 1 and 2 of the drawing, the lam comprises a pear-shaped outer glass envelope I having a neck 2 and a reentrant stem 3. A screw type base i is mounted on the neck 2 and a pair of lead-in wires and 6 are connected to the usual contacts on the base 4 and extend through the press I of the stem 3 into the interior of the envelope I for conducting electricity to the arc tube 8 mounted within the envelope I. The latter is provided with a reflecting coating 8, such as vaporized aluminum, covering its inner surface from its neck 2 to its part of greatest diameter to control the light emitted by the discharge in the arc tube.

The are tube 8 is of a well-known commercial type and comprmes a tubular envelope of high softening point material, such as quartz, having two main discharge supporting electrodemlil and II mounted at its ends and an auxiliary electrode I2 mounted adjacent the main electrode Iiiand connected to the other electrode II through a resistance I3 for starting purposes. The electrodes are sealed into the envelope by the usual sealing glass. The tube contains a starting gas at a few millimeters pressure and mercury in such an amount that it is completely vaporized at a temperature slightly below that at which the tube is designed to operate. During operation the mencury vapor pressure is sufficient to constrict the discharge so that it appears as a luminous chord or thread of high brightness along the axis of the tube. The outer envelope I protects the arc tube 8 from drafts or the like during operation and encloses the inner conducting parts of the lamp. It is usually filled with a gas, such as nitrogen.

It is necessary to firmly support the tube 8 in predetermined relation to the reflecting surface 8 on the envelope I and to offer the minimum oh- 2 struction to the light emitted by the discharge in the tube 8.

The are tube mount shown in Figs. 1 and 2 of the drawing combines both of these features and is highly practical to manufacture. The .mount supports the arc tube, coaxially with the envelope 2 independently of the lead-in wires 5 and 6 and comprises three spaced support wires or legs I4, I5 and I8 attached, as by welding, to a clamp I'I around the stem 3 of the envelope I to provide the rigidity of support that a tripod affords. The clamp I1 is provided with a nut I8 and bolt I9 by which it may be tightened around the stem 3. In addition, the portions of the support wire I4, I5 and I6 extending opposite the arc tube 8 are twisted helically about 120 which also adds to the strength of the mount as well as minimizing shadows cast thereby.

A pair of triangular-shaped bridging supports 20 and 2| having central openings 22 of smaller diameter than that of the arc tube 8 engage and resiliently clamp the arc tube between them and are attached to each of the support wires I4, I5 and I6. The bridging supports 20 and 2| are perforated adjacent each of their corners and the support wires l4, I5 and I6 extend through the perforations. The corners 23 of the bridging supports are bent outward from the arc tube and are attached to the support wires by welding, for example.

The operating current is supplied to the upper main discharge supporting electrode I0 through the in-lead wire 5 extending through and her-metically joined to the press I, the flexible lead wire 24 and in-lead wire 25 extending through, hermetically joined to the end of the arc tube 8 by a sealing glass and supporting the electrode I0. The operating current is supplied to the lower wmain discharge supporting electrode I I through the in-lead wire Ii, the flexible lead wire 26, the support wire I5, the lower flexible lead wire 21 which is attached to the in-lead wire 28 extending through the lower end of the arc tube and sup porting the electrode I I. The auxiliary electrode I2 is electrically connected to the main electrode II by the in-lead wire 29 extending through the end of the arc tube, the flexible lead 30 and the resistance element I3 which is supported by a rigid lead 3i welded to the support wire I5 which is electrically connected to the lower main discharge supporting electrode I I.

The outer glass envelope I is made up of a spherical lower portion 32 merging with a conical upper portion 33 which joins the cylindrical neck 2. For purposes of controlling the distribution accuses oithelightfromthel discharleintube uminous l to obtain maximum utilization oi illumination on a work plane. it is desirable that most or the light from the lamp be reflected by the coating I. Accordingly. in a 400 watt lamp made by me, the center of the are between electrodes II and II was mounted about 2 above the plane including the maximum diameter part or the lamp envelope, the quartz-envelope or the arc tube was approximately 4%" long with a gap of 2%" between the main electrodes III and II, the maximum outer diameter of the envelope I was approximately 6 /2" and the distance between the plane including the part or maximum diameter of the envelope I and the plane including the base of the neck 2 was approximately 4 The overall length or the lamp was approximately 11 /2". Thus, the arc gap was surrounded by the conical reflecting coating 8 and was shielded from view at an angle of approximately 20 measured from the bottom of the gap to the plane including bottom edge of the reflecting coating 9. Further, practically all the light passed through the spherical portion 32 of the envelope I on first reflection and practically no radiant energy was reflected back to the upper glass beads sealing the in-leads 25 and 29 into the quartz envelope of the arc tube 8 which is highly desirable in avoiding cracking of the seal caused by overheating.

In Fig. 3 of the drawing 1 have illustrated another form of outer envelope 35 which may be used in place of the envelope I of Fig. 1. The part 36 of the glass envelope 35 covered by the reflecting coating, such as coating 9, is of paraboloidal contour and the lower, light-transmitting part 31 thereof is dish shaped. The maximum diameter of the envelope 35 and the distance between the planes including the base f its neck 38 and its part of maximum diameter may be the same as in the envelope I of Fig. 1. Also, the arc tube 8 may be mounted in the same position relative to said planes and in the axis of the envelope 35.

The light-transmitting lower parts 32 and 31 of the outer envelopes I and 35 respectively may be clear or slightly frosted.

What I claim as new and desire to secure by Letters Patent of the United States is:

l.In an electric discharge lamp having an outer envelope provided with an reentrant stem having current lead-in wiresextending there.- through and an inner tubular envelope having a' light source therein, a tripod mount attached to said inner envelope and including a clamp en gaging said stem to support said inner envelope independently or said lead-in wires and within and in spaced relation to said outer envelope and having legs attached to said clamp and extending from end-to-end of and spaced from and about said inner envelope, the portions 0! said legs opposite said envelope being helically twisted an angular distance or about to increase the strength or the tripod mount and to minimise shadows cast thereby.

2. In an electric discharge lamp having an outer envelope provided with a reentrant stem havinl current lead-in wires extending therethrough and an inner tubular envelope having a lilht source therein, a tripod mount attached to said inner envelope and including a clamp engaging said stem to support said inner envelope independently of said lead-in-wlres and within and in spaced relation to said outer envelope and having legs attached to said clamp and extending from endto-end of and spaced from and about said inner envelope, the portions of said legs opposite said envelope being helically twisted an angular distance of about 120 to increase the strength of the tripod mount and to minimize shadows cast thereby, said mount including also triangular supports engaging the ends of the inner envelope and having corners attached to each of said legs.

ERNEST C. MAR'I'I.

REFERENCES crran The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,152,997 Johnson A r. 4, 1939 FOREIGN PATENTS Number Country Date 398,829 Great Britain Sept. 19, 1933 

